1. Field of the Invention
The present invention relates to an endoscope apparatus equipped with an image pickup apparatus, and more particularly, to an endoscope apparatus capable of preventing fogging, condensation or the like on the surface of an objective optical system provided to observe a subject.
2. Description of the Related Art
As is well known, endoscope apparatuses are widely used for observation, treatment or the like of the inside of the body (inside the body cavity) of a living body or inspection, repair or the like inside industrial plant equipment. In recent years, electronic endoscope apparatuses equipped with an image pickup apparatus such as a CCD are the mainstream among endoscope apparatuses.
Furthermore, an endoscope apparatus may be subject to fogging in its objective optical system caused by condensation produced due to a temperature difference between an outside air temperature and ambient temperature of a subject to be examined or ambient humidity of the subject to be examined or the like. Therefore, various kinds of technique are proposed to prevent fogging, condensation or the like from occurring in objective optical systems of endoscope apparatuses.
For example, an image pickup apparatus of an endoscope disclosed in Japanese Patent Application Laid-Open Publication No. 2003-284686 is configured such that an air gap is provided between a CCD and a cover glass, a peripheral circuit is disposed above the outer surface located on the prism side of the cover glass so that heat generated from this peripheral circuit is constantly transmitted to the cover glass. Thus, according to Japanese Patent Application Laid-Open Publication No. 2003-284686, when the observation optical system is drastically cooled with cleaning water jetted over an observation window, the cover glass cooled via a lens barrel and the prism receives heat from the peripheral circuit, which reduces the temperature difference between the outer surface located on the prism side and the inner surface located on the air gap side, preventing fogging on the inner surface caused by moisture in the air gap.
Furthermore, for example, in an anti-fogging apparatus of a rigid endoscope disclosed in Japanese Patent Application Laid-Open Publication No. 2003-334157, a heating light guide is inserted into an insertion portion of the rigid endoscope and a dual function light-shielding/heat transfer metal plate that shields light guided by the heating light guide and converts the shielded light to heat warms a light receiving lens and thereby prevents fogging from occurring on the light-receiving lens.